Potentiometric and electrochemical sensor devices have received great attention in the last few years. In the recent past there has been widespread focus on miniaturization and patterning of these sensor devices from bulk to microchips scale.
One of the goals of a manufacturer of electrochemical sensors is to produce sensors that are sufficiently cheap and can be deployed as unit-use devices, thus eliminating or simplifying the analyzer's often very complex fluidics required for the washing and calibrating of multiple-use sensors. To achieve this goal, manufacturers have investigated planar technologies for low cost sensor manufacture. Such planar technologies also purport to provide appropriate control of the materials of construction and manufacturing processes to achieve device-to-device reproducibility in high volume production. Sensors made by planar technology include both thick-film and thin-film micro-fabrication technologies. Thick film processed devices comprise electrodes made by thick film fabrication processes such as plating, screen-printing and dispensing among others. Micro-fabrication technology has proven to have superior dimensional control and has been used to make devices for unit-use applications. Micro-fabrication technology employs wafer-level processes and these devices contain electrodes made by thin-film micro-fabrication processes on various substrates.
Micro-fabrication methodologies of the miniaturized microchips are mainly based on the deposition of a sensitive membrane layer on a micro-sized substrate. In this context, screen-printing is a well-known technique in the micro-fabrication method for realizing micro-sensor assemblies on various substrates (i.e., plastic, ceramics, paper, glass, etc.) [1-3]. Solid-state square planar electrodes particularly screen printed microchips are substrates widely used in the fabrication of chemical sensors responsive for biological species, drugs, toxic elements or heavy metals. These devices with plastic substrates are coated with layers of electro-conductive and insulating inks at a controlled thickness. The screen-printed technology is a modern technology having superior features namely, simple, fast, integration and automation feasibility and can be used in vivo applications. The advantages provided by the screen-printed electrodes are short response times, accuracy, robust, inexpensive, use of small amounts of reagents, miniaturization, large-scale production, small size, disposability, low output impedance and low cost by mass production. Regardless of which of the above variants of planar technology is being used, planar devices of the prior art have been complex to manufacture and are therefore still relatively expensive. In addition in spite of the mentioned advantages of the screen-printed based micro-sensors, such technology is rather rarely applied for the fabrication of potentiometric devices.
In order to improve the selectivity of the potentiometric sensors and ion selective electrodes, significant research effort has been focused on the development and modification of these sensors with nano-particle based sensitive layers [4-11]. Such materials have unique properties and improve the potentiometric response of the electrodes due to the high surface to volume ratio, which is a characteristic feature of such materials [5,6]. Sensitive organic membrane layers generally applied in the fabrication of a huge number of chemical sensors have the advantages of high sensitivity, fast response time and being highly selective. The deposition of a sensitive organic membrane layer on the surface of disposable plastic screen-printed microchips is a big challenge and requires sophisticated technological strategies including highly professional servicing. Great attention has been paid and many attempts have been made by scientists to fabricate plastic screen-printed microelectrodes with a sensitive organic membrane layer. Unfortunately, most of these attempts have failed and have not been successful.
It has been noticed over time that the need for the assessment of toxic metals and in particular lead has increased tremendously and has gained significant importance due to the harmful effects of lead on the environment and to human beings. The methods for the determination of lead and other toxic elements, that are in current use that are disclosed in the prior art require sophisticated and expensive machines.
Based on the above-mentioned facts, fabrication, characterization and application of the screen-printed based electrodes to determine lead has become a very interesting challenge for many scientists. Various screen printed modified electrodes have been reported to present promising and cost effective devices for accurate and precise analysis of environmental, biomedical and industrial interest species in different disciplines of samples [12-16].
The present invention discloses a method to fabricate a type of screen-printed microchip based on a nanostructure sensitive organic membrane layer, which is responsive to lead(II). The nano-composite material is embedded in a plasticized PVC membrane and is deposited on the surface of a microchip substrate using a novel, simple, fast and economical approach. The resulting lead(II) screen-printed microchip provides high sensitivity, fast response time, simple fabrication, low cost and automation and integration feasibility. It represents a simple, cheap, miniaturized and mass production tool or device for lead(II) measurements. The micro-fabrication, potentiometric characterization and analytical application of the prepared sensor are demonstrated in this invention.
It would be desirable to provide improved sensor devices. For example, it would be advantageous to improve sensing accuracies, increase production and operation efficiencies, and extend the useful life of the sensor, while minimizing the device size for ease of use and cost of manufacture. The present invention discloses a method and application to achieve the desirable qualities of an electrochemical sensor.